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Abstract:

Provided is a communication terminal that prevents a listener from
missing a conversation during a group call and enables the listener to
identify a speaker. Mobile telephones of users B and C receive, from a
mobile telephone of a user A who is a speaker, DTMF information having a
value of "1" and identifying the user A, and audio data of the user A;
output an identification tone indicated by the DTMF information, and
audio of the user A; and store the DTMF information and a flag indicating
"other". When a speaker is switched to the user B, the mobile telephone
of the user B generates audio data of the user B, selects DTMF
information having a value of "2" as information identifying the user B;
and transmits the selected DTMF information and the audio data of the
user B to the mobile telephones of the users A and C.

Claims:

1. A communication terminal used for a group call, comprising: a
reception unit configured to receive first identification tone
information and first audio data from another communication terminal
within a group of communication terminals participating in the group
call, the first identification tone information indicating a first
identification tone for said another communication terminal, and the
first audio data pertaining to the group call; an output unit configured
to output the first identification tone, and audio based on the first
audio data; an audio input unit configured to receive an input of audio
pertaining to the group call; and a transmission unit configured to
transmit second identification tone information and second audio data to
all communication terminals within the group other than the communication
terminal, the second identification tone information indicating a second
identification tone for the communication terminal, and the second audio
data indicating the audio received by the audio input unit.

2. The communication terminal of claim 1, further comprising: a key input
unit having a group of keys and configured to detect whether a user has
pressed a predetermined key from among the group of keys, wherein the
transmission unit transmits the second identification tone information
and the second audio data when pressing of the predetermined key has been
detected by the key input unit.

3. The communication terminal of claim 2, wherein the key input unit is
further configured to detect whether the predetermined key pressed by the
user has been released, and the audio input unit receives the input of
the audio pertaining to the group call during a period from detection of
the pressing of the predetermined key to detection of the release of the
predetermined key.

4. The communication terminal of claim 1, further comprising: a storage
unit configured to store information; a determination unit configured to
determine whether the same identification tone information as the first
identification tone information is stored in the storage unit; and a
control unit configured to, when the determination unit determines that
the same identification tone information is not stored in the storage
unit, cause the first identification tone information to be stored into
the storage unit as identification tone information indicating an
identification tone identifying said another communication terminal which
has transmitted the first identification tone information.

5. The communication terminal of claim 4, wherein the control unit is
further configured to delete all identification tone information stored
in the storage unit when the group call is ended.

6. The communication terminal of claim 4, wherein the determination unit
is further configured to determine whether the second identification tone
information is stored in the storage unit, and the control unit is
further configured to, when the determination unit determines that the
second identification tone information is not stored in the storage unit,
cause the second identification tone information to be stored into the
storage unit as identification tone information indicating an
identification tone identifying the communication terminal.

7. The communication terminal of claim 1, wherein the reception unit
receives, as the first identification tone information, information
resulting from coding of a first DTMF tone, the output unit outputs the
first DTMF tone as the first identification tone, and the control unit
transmits, as the second identification tone information, information
resulting from coding of a second DTMF tone.

8. The communication terminal of claim 1, wherein the reception unit
receives, as the first identification tone information, information
indicating a first DTMF tone, and the output unit holds correspondence
information indicating a one-to-one correspondence between (i) pieces of
identification tone information each indicating a different DTMF tone and
(ii) a plurality of musical notes each assigned to a different one of the
pieces of the identification tone information, selects, with use of the
correspondence information, one of the musical notes that corresponds to
the first identification tone information, and outputs a tone indicated
by the selected musical note as the first identification tone.

9. A communication method used in a communication terminal, the
communication terminal being for a group call and including a reception
unit, an output unit, an audio input unit, and a transmission unit, the
communication method comprising the steps of: the reception unit
receiving first identification tone information and first audio data from
another communication terminal within a group of communication terminals
participating in the group call, the first identification tone
information indicating a first identification tone for said another
communication terminal, and the first audio data pertaining to the group
call; the output unit outputting the first identification tone, and audio
based on the first audio data; the audio input unit receiving an input of
audio pertaining to the group call; and the transmission unit
transmitting second identification tone information and second audio data
to all communication terminals within the group other than the
communication terminal, the second identification tone information
indicating a second identification tone for the communication terminal,
and the second audio data indicating the audio received by the audio
input unit.

10. A computer-readable recording medium storing thereon a communication
program for causing a computer to function as a communication terminal
used for a group call, the communication program causing the computer to
function as: a reception unit configured to receive first identification
tone information and first audio data from another communication terminal
within a group of communication terminals participating in the group
call, the first identification tone information indicating a first
identification tone for said another communication terminal, and the
first audio data pertaining to the group call; an output unit configured
to output the first identification tone, and audio based on the first
audio data; an audio input unit configured to receive an input of audio
pertaining to the group call; and a transmission unit configured to
transmit second identification tone information and second audio data to
all communication terminals within the group other than the communication
terminal, the second identification tone information indicating a second
identification tone for the communication terminal, and the second audio
data indicating the audio received by the audio input unit.

Description:

[0001] The disclosure of Japanese Patent Application No. 2012-014499 filed
Jan. 26, 2012 including specification, drawings and claims is
incorporated herein by reference in its entirety.

TECHNICAL FIELD

[0002] The present invention relates to a communication terminal, and in
particular to a technique for assisting listeners to identify a speaker
during a group call.

BACKGROUND ART

[0003] In recent years, a PTT (Push To Talk) system has been widely used.
In the PTT system, a telephone conversation is not conducted on a
one-to-one basis as seen in a general telephone conversation. Instead, a
plurality of communication terminals constitute a group, and audio is
transmitted from one of the communication terminals within the group to
all the rest of the communication terminals within the group. The PTT
system uses a transceiver communication system, whereby a speaker can
transmit audio only while a PTT button of a communication terminal is
being pressed. A listener receives audio from any speaker within the
group. Accordingly, the listener needs to identify the current speaker
based on, for example, his/her voice or the name of the speaker shown on
a display of a communication terminal of the listener.

CITATION LIST

Patent Literature

[Patent Literature 1]

[0004] Japanese Patent Application Publication No. 2006-246201

SUMMARY OF INVENTION

[0005] However, when a listener identifies a speaker based on his/her
voice, the accuracy in identifying the speaker may be greatly degraded by
uncertainties, such as the listener's ability to identify the speaker and
the way the speaker speaks. Also, suppose that the listener identifies a
speaker by checking the name of the speaker shown on the display of the
communication terminal In such a case, since the speaker constantly
changes, the listener needs to constantly check the display during a PTT
call, and to focus on checking the display. As a result, when the
listener moves the receiver away from his/her ear to check the display,
the listener may miss part of what the speaker is saying.

[0006] The present invention has been achieved in view of the above
problems, and an aim thereof is to provide a communication terminal that
prevents a listener from missing a conversation during a group call, and
that enables the listener to easily identify a speaker.

[0007] In order to solve the above problems, the present invention
provides a communication terminal used for a group call, comprising: a
reception unit configured to receive first identification tone
information and first audio data from another communication terminal
within a group of communication terminals participating in the group
call, the first identification tone information indicating a first
identification tone for said another communication terminal, and the
first audio data pertaining to the group call; an output unit configured
to output the first identification tone, and audio based on the first
audio data; an audio input unit configured to receive an input of audio
pertaining to the group call; and a transmission unit configured to
transmit second identification tone information and second audio data to
all communication terminals within the group other than the communication
terminal, the second identification tone information indicating a second
identification tone for the communication terminal, and the second audio
data indicating the audio received by the audio input unit.

[0008] With the above structure, the communication terminal of the present
invention can prevent a listener from missing a conversation during a
group call, and enables the listener to easily identify a speaker.

BRIEF DESCRIPTION OF DRAWINGS

[0009] FIG. 1 schematically shows the structure of a PTT system according
to an embodiment of the present invention.

[0010] FIG. 2 shows the internal structure of a mobile telephone according
to the embodiment of the present invention.

[0011] FIGS. 3A to 3C are for explaining DTMF information according to the
embodiment of the present invention. FIG. 3A shows a DTMF matrix, FIG. 3B
shows a note table, and FIG. 3c shows an in-use DTMF table.

[0012] FIG. 4 illustrates update of the in-use DTMF table according to the
embodiment of the present invention, where (a) explains a case where a
user A starts a PTT call and transmits audio, (b) explains a case where a
user B further transmits audio after the user A, (c) explains a case
where the user A further transmits audio after the user B, and (d)
explains a case where a user C further transmits audio after the user A.

[0013]FIG. 5 is a flow chart showing a PTT execution process according to
the embodiment of the present invention.

[0014]FIG. 6 is a flowchart showing a PTT call process according to the
embodiment of the present invention.

[0015] FIG. 7 is a flowchart showing a PTT participation process according
to the embodiment of the present invention.

[0016] FIG. 8 shows the internal structure of a PTT server according to
the embodiment of the present invention.

[0017]FIG. 9 is a flowchart showing a process pertaining to a PTT call,
the process being performed by the PTT server according to the embodiment
of the present invention.

[0018] FIG. 10 is a flowchart showing an overall process of the PTT system
during PTT execution according to the embodiment of the present
invention.

DESCRIPTION OF EMBODIMENT

<1. Overview>

[0019] In a PTT system according to an embodiment of the present
invention, a listener in a PTT call can easily identify a speaker without
checking the name of the speaker shown on a display of a mobile telephone
of the listener.

[0020] FIG. 1 schematically shows the structure of a PTT system 1
according to an embodiment of the present invention.

[0021] The PTT system 1 includes mobile telephones 2a, 2b, 2c, . . . , a
PTT server 3, and a communication network 5. Each of the mobile
telephones 2a, 2b, and 2c is one example of a communication terminal used
in a PTT call. The communication network 5 includes a mobile telephone
network such as base stations 4a, 4b, . . . , and a network such as the
Internet. The PTT server 3 performs management pertaining to a PTT call.
Hereinafter, the mobile telephones 2a, 2b, 2c, . . . are collectively
referred to as mobile telephones 2, and the base stations 4a, 4b, . . .
are collectively referred to as base stations 4, unless distinction is
necessary.

[0022] In the following description, a PTT call is started by the mobile
telephone 2a within a group consisting of the mobile telephones 2a, 2b,
and 2c (hereinafter "PTT group").

[0023] A user A of the mobile telephone 2a selects the mobile telephones
2b and 2c by operating an input device (e.g., keypad) of the mobile
telephone 2a, and instructs the mobile telephones 2b and 2c to start the
PTT call.

[0024] The mobile telephone 2a designates the mobile telephones 2b and 2c
as the terminals to be included in the PTT call, and transmits a request
for starting the PTT call to the PTT server 3.

[0025] The PTT server 3 registers the mobile telephones 2a, 2b, and 2c as
a PTT group, and transmits a PTT start instruction to the mobile
telephones 2a, 2b, and 2c. The mobile telephones 2a, 2b, and 2c receive
the PTT start instruction and become ready to start the PTT call.

[0026] Here, the user of the mobile telephone 2a presses a PTT button of
the mobile telephone 2a, and inputs audio to a microphone of the mobile
telephone 2a.

[0027] Upon detecting that the PTT button is pressed, the mobile telephone
2a selects a DTMF (Dual-Tone Multi-Frequency) tone not used by the other
mobile telephones, generates audio data by encoding the audio input to
the microphone, and transmits DTMF information indicating the DTMF tone
and the audio data to the PTT server 3.

[0028] Upon receiving the DTMF information and the audio data, the PTT
server 3 transfers the DTMF information and the audio data to the mobile
telephones 2b and 2c. Each of the mobile telephones 2a, 2b, and 2c holds
a note table indicating the correspondence between DTMF information and
note information indicating a note such as Do, Re, or Mi. Upon receiving
the DTMF information and the audio data, each of the mobile telephones 2b
and 2c outputs, to a receiver, (i) a tone (i.e., an identification tone
for identifying the user A of the mobile telephone 2a) indicated by a
note (e.g., "Do") corresponding to the received DTMF information and (ii)
audio obtained by decoding the received audio data.

[0029] Suppose that a user B of the mobile telephone 2b presses a PTT
button of the mobile telephone 2b, and inputs audio to a microphone of
the mobile telephone 2b. In this case, similarly to the case of the
mobile telephone 2a, each of the mobile telephones 2a and 2c outputs, to
a receiver, (i) a tone (i.e., an identification tone for identifying the
user B of the mobile telephone 2b) indicated by a note (e.g., Re)
corresponding to received DTMF information and audio obtained by decoding
received audio data.

[0030] When a user C of the mobile telephone 2c presses a PTT button of
the mobile telephone 2c, and inputs audio to a microphone of the mobile
telephone 2c, the same process as in the mobile telephones 2a and 2b is
performed.

[0031] Regarding DTMF information, each of the mobile telephones 2a, 2b,
and 2c exchanges information with the other mobile telephones, and
selects DTMF information indicating a DTMF tone not used by the other
mobile telephones. Each of the mobile telephones 2a, 2b, and 2c uses the
individually selected DTMF information until the PTT call is ended.

[0032] Accordingly, when audio produced by the user of the mobile
telephone 2a is output from the receivers of the mobile telephones 2b and
2c, the identification tone indicated by the note "Do" is output first
before the audio, and thereafter the audio of the user of the mobile
telephone 2a is output.

[0033] Similarly, when audio produced by the user of the mobile telephone
2b is output from the receivers of the mobile telephones 2a and 2c, the
identification tone indicated by the note "Re" is output first before the
audio, and thereafter the audio of the user of the mobile telephone 2b is
output.

[0034] Similarly, when audio produced by the user of the mobile telephone
2c is output from the receivers of the mobile telephones 2a and 2b, the
identification tone indicated by the note "Mi", for example, is output
first before the audio, and thereafter the audio of the user of the
mobile telephone 2c is output.

[0035] As described above, the user of a mobile telephone 2 can listen to
a tone (speaker identification tone) which is output before audio
transmitted from another mobile telephone 2 is output. This enables the
user to identify a speaker who has transmitted the audio.

<2. Structure>

<2-1. Mobile Telephone 2>

[0036] The following describes one of the mobile telephones 2.

[0037] Specifically, the mobile telephone 2 is a computer system composed
of a microprocessor, a ROM (Read Only Memory), a RAM (Random Access
Memory), etc. The RAM stores therein a computer program. The mobile
telephone 2 achieves its function by the microprocessor operating in
accordance with the computer program.

[0038] FIG. 2 shows the internal structure of the mobile telephone 2.

[0039] As shown in FIG. 2, the mobile telephone 2 includes a microphone
11, a receiver 12, a display 13, an input unit 14, a communication
antenna 15, a wireless communication unit 16, a signal processing unit
17, a notification control unit 18, a speaker 19, a display control unit
20, a storage unit 21, and a control unit 22.

[0040] During a call, the microphone 11 collects audio produced by the
user, converts the audio into a call signal, which is an electrical
signal, and transmits the call signal to the signal processing unit 17.

[0041] The receiver 12 receives audio signal generated by the signal
processing unit 17, converts the audio signal into audio, and outputs the
audio so that the user can listen to the audio.

[0042] The display 13 displays video and images. For example, the display
13 is composed of a liquid crystal display. The display 13 receives a
video signal generated and output by the display control unit 20, and
displays video pertaining to the video signal. For example, the video
signal is generated from characters, images, video, etc.

[0043] The input unit 14 is an input device for the user to input
instructions to the mobile telephone 2. The input unit 14 notifies the
control unit 22 of the instructions input thereto. For example, the input
unit 14 includes a keypad and a touch panel. The keypad is composed of a
PTT button, a group of keys, etc.

[0044] The PTT button is normally in a convex state. The PTT button is
placed in a concave state only while being pressed by the user, and
returns to a convex state when being released by the user. While the PTT
button is in a pressed state during a PTT call, audio is transmitted from
the mobile telephone 2 to the other mobile telephones 2. When the PTT
button is in a released state, the mobile telephone 2 receives audio from
the other mobile telephones 2. In other words, while speaking, the user
presses the PTT button. When finishing the speaking and enabling
reception of audio from the other mobile telephones 2, the user releases
the PTT button. The input unit 14 detects whether the PTT button is in a
pressed state or in a released state, and outputs, to the control unit
22, PTT state information indicating whether the PTT button is in a
pressed state or in a released state.

[0045] The communication antenna 15 is used for a wireless communication
between the base stations 4 that constitute the mobile telephone network.

[0046] The wireless communication unit 16 performs a wireless
communication with the base stations 4 via the communication antenna 15.
The wireless communication unit 16 demodulates a signal received from any
of the base stations 4, generates a baseband signal from the received
signal, and transmits the baseband signal to the signal processing unit
17. Also, the wireless communication unit 16 modulates a baseband signal
received from the signal processing unit 17, and transmits the modulated
signal to any of the base stations 4.

[0047] The signal processing unit 17 restores additional data, DTMF
information, and audio data from the baseband signal received from the
wireless communication unit 16. The additional data is used for
conversations and communications during a PTT call. During reception of
audio, the additional data includes the mobile telephone number of a
person who is transmitting the audio, and the mobile telephone numbers of
the other people who are also receiving the audio. During transmission of
audio, the additional data includes the own mobile telephone number and
the mobile telephone numbers of the people who are receiving the audio.

[0048] DTMF tones are synthesized tones. Each DTMF tone is made up of two
signals, one of which belongs to a high group (unit: Hz) consisting of
signals each having a high frequency, and the other of which belongs to a
low group (unit: Hz) consisting of signals each having a low frequency.
Each synthesized tone is used as a push tone when a corresponding key
(e.g., the key of number "1") is pressed. Hereinafter, information
indicating a DTMF tone is referred to as DTMF information.

[0049] FIGS. 3A to 3C are for explaining DTMF information.

[0050]FIG. 3A shows a DTMF matrix indicating the correspondence between
(i) the high group and the low group and (ii) the DTMF information.

[0051] For example, a tone (DTMF tone) resulting from the combination of a
signal of 1209 Hz in the high group and a signal of 697 Hz in the low
group is associated with the DTMF information having a value of "1".
Here, the value of DTMF information corresponds to the number of a key.
For example, the DTMF information having a value of "1" corresponds to
the key of number "1". A tone resulting from the combination of a signal
of 1209 Hz in the high group and a signal of 941 Hz in the low group is
associated with the DTMF information having a value of "*", and
corresponds to the key of the symbol "*" from among the group of keys.
Also, a tone resulting from the combination of a signal of 1633 Hz in the
high group and a signal of 697 Hz in the low group is associated with the
DTMF information indicating an alphabet of "A". Note that the group of
keys does not include any key that indicates an alphabet such as "A".
Therefore, in the DTMF matrix, a DTMF tone associated with an alphabet or
a symbol that is not indicated by any key in the group may be associated
with a button other than the group of keys, and may be used as a push
tone when the button is pressed.

[0052] When DTMF information is restored from a baseband signal, the
signal processing unit 17 outputs the DTMF information to the control
unit 22 and receives note information corresponding to the DTMF
information from the control unit 22. As described above, note
information indicates a note in a predetermined musical scale (e.g.,
"Do", "Re", etc.), and the control unit 22 converts the DTMF information
into note information with use of the note table.

[0054] For example, the DTMF information having a value of "1" corresponds
to the note "Do".

[0055] In the figure, the note indicated by the note information is
"Dom (m being a natural number)". The number "m" ("1" in the present
example) after the note "Do" is added for convenience in order to
distinguish between "Do" (e.g., Do1) and "Do" of one octave higher
(e.g., the note "Do2" corresponding to the DTMF information having a
value of "B").

[0056] Upon receiving note information from the control unit 22, the
signal processing unit 17 first outputs, to the receiver 12, an audio
signal indicating an identification tone (e.g., "Do") of the note
indicated by the note information, and then outputs, to the receiver 12,
an audio signal indicating the audio indicated by received audio data. At
this time, the receiver 12 first outputs the tone of "Do", and thereafter
the audio. As described above, before output of audio produced by the
user of another mobile telephone, a speaker identification tone (the tone
of the note "Do" in the present example) identifying the user is output
first from the receiver 12. Regarding such an identification tone, a
different note is assigned to each user (each mobile telephone) so as to
help the listeners in a PTT call to identify the speaker. Here, the
control unit 22 converts DTMF information to note information. This is
because a tone indicated by a note is generally more well-known than a
DTMF tone, and as such, it is considered to be easier for the user to
identify a speaker based on note information.

[0057] Upon receiving, from the control unit 22, an audio transmission
instruction generated by the PTT button being pressed, the signal
processing unit 17 receives, from the microphone 11, an audio signal
indicating audio produced by the user and encodes the audio signal to
generate audio data. Also, the signal processing unit 17 receives, from
the control unit 22, DTMF information and additional data necessary for
communication; generates a baseband signal for transmitting the
additional data, the DTMF information, and the audio data; and transmits
the baseband signal to the wireless communication unit 16.

[0058] The notification control unit 18 controls notifications to the
user. The notification control unit 18 gives a notification upon
receiving an incoming call, upon receiving a PTT start instruction, and
so on. The notification control unit 18 gives a notification by
outputting, to the speaker 19, an audio signal indicating a notification
tone associated with the notification from among a plurality of
notification tones each associated with a different notification, and
causes the speaker 19 to output the notification tone.

[0059] The display control unit 20 performs control so as to display
images or video on the display 13. For example, the display control unit
20 generates video to be displayed on the display 13, and outputs a
signal indicating the video to the display 13.

[0060] The storage unit 21 stores various pieces of information, such as
an address book, an in-use DTMF table, etc.

[0061] The address book includes user names, mobile telephone numbers,
mail addresses, and other information in association with each other.

[0063] The in-use DTMF table is a list of in-use DTMF entries, each
consisting of DTMF information and a self/other flag. Each in-use DTMF
entry corresponds to a different mobile telephone in a PTT call. The
self/other flag indicates whether DTMF information is associated with the
own mobile telephone 2 (i.e., "self") or any of the other mobile
telephones 2 (i.e., "other") in the PTT call. Until a PTT call is
started, the in-use DTMF table is blank and does not include any in-use
DTMF entry.

[0064] When a PTT call is started, an in-use DTMF entry is recorded into
the in-use DTMF table. Then, as a conversation in the PTT call
progresses, the in-use DTMF table keeps being updated. When the PTT call
is ended, all in-use DTMF entries are deleted from the in-use DTMF table.

[0066] In FIG. 4, the respective in-use DTMF tables of the mobile
telephone 2a of the user A, the mobile telephone 2b of the user B, and
the mobile telephone 2c of the user C are updated in a time sequence in
the order of (a), (b), (c), and (d) as the PTT call progresses.

[0067] The user A starts a PTT call, and the users B and C participate in
the PTT call.

[0068] In FIG. 4, (a) shows the in-use DTMF table of each mobile telephone
when the user A has started the PTT call and transmitted audio.

[0069] When starting the PTT call and transmitting audio, the mobile
telephone 2a of the user A selects a DTMF tone indicated by the DTMF
information having a value of "1", and records, into the in-use DTMF
table, an in-use DTMF entry consisting of the DTMF information and a
self/other flag indicating "self". Here, the mobile telephone 2a selects
the DTMF tone corresponding to the value "1". However, this is merely an
example, and the mobile telephone 2a may select any DTMF tone as long as
it is not recorded in the in-use DTMF table. The mobile telephone 2a
transmits the DTMF information (1) corresponding to the selected DTMF
tone to the mobile telephones 2b and 2c of the users B and C who are
participating in the PTT call. Here, DTMF information (n) (n being a
natural number) denotes DTMF information having a value of "n". Each of
the mobile telephones 2b and 2c receives the DTMF information (1), and
records, into its own in-use DTMF table, an in-use DTMF entry consisting
of the DTMF information (1) and a self/other flag indicating "other"
(hereinafter "other flag"). As a result, the in-use DTMF tables held by
the mobile telephones 2a, 2b, and 2c are placed in their respective
states as shown by in-use DTMF tables 61, 71, and 81.

[0070] With the above process, the mobile telephone 2a recognizes that the
DTMF information having a value of "1" is assigned thereto, and the
mobile telephones 2b and 2c recognize that the DTMF information having a
value of "1" is assigned to another mobile telephone.

[0071] In FIG. 4, (b) shows the in-use DTMF table of each mobile telephone
after the state shown in (a), where the user B has further transmitted
audio after the user A.

[0072] When transmitting audio, the mobile telephone 2b of the user B
selects a DTMF tone different from the DTMF tone indicated by the DTMF
information having a value of "1" which is already stored in the in-use
DTMF table. Then, the mobile telephone 2b records, into the in-use DTMF
table, an in-use DTMF entry consisting of the DTMF information indicating
the selected DTMF tone (the DTMF information having a value of "2" in the
present example) and a self/other flag indicating "self" (hereinafter
"self flag"). Subsequently, the mobile telephone 2b transmits the DTMF
information (2) indicating the selected DTMF tone to the mobile
telephones 2a and 2c. Each of the mobile telephones 2a and 2c receives
the DTMF information (2), and records, into its own in-use DTMF table, an
in-use DTMF entry consisting of the DTMF information (2) and an other
flag. If the same information as the received DTMF information (2) is
already stored in the in-use DTMF table of each of the mobile telephones
2a and 2c, the mobile telephones 2a and 2c do not record the DTMF
information (2). As a result, the in-use DTMF tables held by the mobile
telephones 2a, 2b, and 2c are placed in their respective states as shown
by in-use DTMF tables 62, 72, and 82.

[0073] With the above process, the mobile telephone 2a recognizes that the
DTMF information (1) is assigned thereto, and that the DTMF information
(2) is assigned to another mobile telephone. Also, the mobile telephone
2b recognizes that the DTMF information (2) is assigned thereto, and the
DTMF information (1) is assigned to another mobile telephone.
Furthermore, the mobile telephone 2c recognizes that the DTMF information
(1) and the DTMF information (2) are assigned to the other mobile
telephones.

[0074] In FIG. 4, (c) shows the in-use DTMF table of each mobile telephone
after the state shown in (b), where the user A has further transmitted
audio after the user B.

[0075] The mobile telephone 2a of the user A recognizes that the self flag
is already recorded in the in-use DTMF table thereof, and that the DTMF
information having a value of "1" is assigned thereto. Accordingly, when
transmitting audio, the mobile telephone 2a transmits the DTMF
information (1) corresponding to the self flag to the mobile telephones
2b and 2c. Each of the mobile telephones 2b and 2c does not record the
transmitted DTMF information (1) since the same DTMF information as the
DTMF information (1) is already recorded in its own in-use DTMF table.

[0076] As a result, the in-use DTMF tables held by the mobile telephones
2a, 2b, and 2c are placed in their respective states as shown by in-use
DTMF tables 63, 73, and 83.

[0077] In FIG. 4, (d) shows the in-use DTMF table of each mobile telephone
after the state shown in (c), where the user C has further transmitted
audio after the user A.

[0078] When transmitting audio, the mobile telephone 2c of the user C
selects DTMF information (3) indicating a DTMF tone different from the
DTMF tones indicated by the DTMF information having a value of "1" and
the DTMF information having a value of "2" already stored in the in-use
DTMF table. Then, the mobile telephone 2c records, into the in-use DTMF
table, an in-use DTMF entry consisting of the DTMF information (3) and a
self flag. Subsequently, the mobile telephone 2c transmits the DTMF
information (3) indicating the selected DTMF tone to the mobile
telephones 2a and 2b. Each of the mobile telephones 2a and 2b receives
the DTMF information (3), and records, into its own in-use DTMF table, an
in-use DTMF entry consisting of the DTMF information (3) and an other
flag. As a result, the in-use DTMF tables held by the mobile telephones
2a, 2b, and 2c are placed in their respective states as shown by in-use
DTMF tables 64, 74, and 84.

[0079] With the above process, the mobile telephone 2a recognizes that the
DTMF information (1) is assigned thereto, and that the DTMF information
(2) and the DTMF information (3) are assigned to the other mobile
telephones. Also, the mobile telephone 2b recognizes that the DTMF
information (2) is assigned thereto, and the DTMF information (1) and the
DTMF information (3) are assigned to the other mobile telephones. Also,
the mobile telephone 2c recognizes that the DTMF information (3) is
assigned thereto, and the DTMF information (1) and the DTMF information
(2) are assigned to the other mobile telephones. This completes the
explanation regarding FIG. 4.

[0080] The control unit 22 performs overall control including a process
during a PTT call by the mobile telephone 2. The following describes a
process by the control unit 22 pertaining to a PTT call. The process
includes (i) a PTT execution process, which is performed when the mobile
telephone 2 starts a PTT call; and (ii) a PTT participation process,
which is performed when the mobile telephone 2 participates in a PTT call
started by another mobile telephone.

[0082] First, the user of the mobile telephone 2 operates the input unit
14, and inputs a PTT start instruction (S11). Next, the user selects
users to be included in a PTT call (S12). For example, upon detecting the
input of the PTT start instruction, the control unit 22 displays, on the
display 13, a participant selection screen that is a list of users
registered with the address book. The user of the mobile telephone 2
selects users to which to transmit a PTT participation request, from
among the users shown in the list. Hereinafter, the selected users are
referred to as participating users. Then, the control unit 22 reads the
telephone numbers of the respective participating users from the address
book, and transmits, to the PTT server 3, a PTT start request including
the telephone numbers thus read and the telephone number of its own
(S13).

[0083] Transmission of information from the control unit 22 to the PTT
server 3 is performed as follows. First the signal processing unit 17
encodes the information to be transmitted. The wireless communication
unit 16 transmits the encoded information to a base station 4, which is
one of the base stations 4a, 4b, . . . , with use of the communication
antenna 15. Upon receiving the encoded information, the base station 4
transfers the information to the PTT server 3. Hereinafter, a description
of the above process for transmitting information is omitted to avoid
repetition. Instead, it is simply described as "the control unit 22
transmits information to the PTT server 3". Similarly, regarding
reception of information, it is simply described as "the control unit 22
receives information from the PTT server 3".

[0084] The control unit 22 receives a PTT start instruction, which is
transmitted from the PTT server 3 in response to the PTT start request
(S14), and performs a PTT call process (S15). Details of the PTT call are
described below. As long as a PTT end instruction is not input by the
user using the input unit 14 (S16: No), the control unit 22 continues the
PTT call process. When a PTT end instruction is input (S16: Yes), the
control unit 22 transmits a PTT end request to the PTT server 3, and ends
the PTT execution process.

<PTT Call Process>

[0085]FIG. 6 is a flowchart showing in detail the PTT call process of
step S15.

[0086] The control unit 22 waits for the PTT button to be pressed (S31).
When the PTT button is pressed (S31: Yes), the control unit 22 transmits,
to the PTT server 3, a right-to-speak acquisition request which is a
request for acquiring the right to speak (S32). Upon receiving, from the
PTT server 3 in response to the right-to-speak acquisition request, a
notification indicating that the acquisition of the right to speak has
failed (S33: No), the control unit 22 ends the PTT call process. Upon
receiving, from the PTT server 3, a notification indicating that the
acquisition of the right to speak has been successful (S33: Yes), the
control unit 22 determines whether an in-use DTMF entry including a self
flag (hereinafter "self in-use DTMF entry") is stored in the storage unit
21 (S34). If the self in-use DTMF entry is not recorded in the storage
unit (S34: No), the control unit 22 selects a DTMF tone not recorded in
the in-use DTMF table (S35), and records, into the in-use DTMF table, an
in-use DTMF entry consisting of DTMF information indicating the selected
DTMF tone (hereinafter "self DTMF information") and a self flag (S36).

[0087] Then, the control unit 22 transmits the self DTMF information to
the PTT server 3 (S37). Subsequently, the control unit 22 receives, from
the signal processing unit 17, audio data resulting from encoding of
audio collected by the microphone 11, and transmits the audio data to the
PTT server 3 (S38). At this point, the control unit 22 also transmits, as
additional data, the telephone number of its own. The control unit 22
repeats the process of step S38 until the PTT button is released (S39:
No). When the PTT button is released (S39: Yes), the control unit 22
transmits, to the PTT server 3, a right-to-speak release request which is
a request for releasing the right to speak.

[0088] In step S31, when a press of the PTT button is not detected (S31:
No), the mobile telephone 2 is in a state of receiving audio. In the
state of receiving audio, the control unit 22 determines whether DTMF
information is received (S51). When DTMF information is received (S51:
Yes), the control unit 22 determines whether the DTMF information is
recorded in the in-use DTMF table (S52). When the DTMF information is not
recorded (S52: No), the control unit 22 records, into the in-use DTMF
table, an in-use DTMF entry consisting of the DTMF information and an
other flag (S53). Then, the control unit 22 converts the DTMF information
into note information corresponding thereto with use of the note table
(S54). Next, the control unit 22 causes the receiver 12 to output a
speaker identification tone of a note indicated by the note information
via the signal processing unit 17 (S55). In step S52, when the received
DTMF information is recorded in the in-use DTMF table (S52: Yes), the
process proceeds to step S54.

[0089] Also, when audio data is received from the PTT server 3 (S56: Yes),
the control unit 22 causes the receiver 12 to output audio indicated by
the audio data via the signal processing unit 17 (S57), and ends the PTT
call process.

<PTT Participation Process>

[0090] FIG. 7 is a flow chart showing the PTT participation process.

[0091] When the mobile telephone 2 receives a PTT start request from the
PTT server 3 while a PTT call is yet to be started, the mobile telephone
2 is placed in a PTT participation state which is a state of being
included in a PTT call (S71). Then, the notification control unit 18
causes the speaker 19 to output a notification tone, and the display
control unit 20 displays a screen indicating PTT participation on the
display 13, thereby notifying the user that the mobile telephone 2 is
placed in a PTT participation state (S72). After the notification, the
control unit 22 performs a PTT call process (S73). The process of step
S73 is the same as the PTT call process described with reference to FIG.
6. The control unit 22 continues the PTT call process as long as a PTT
end instruction is not received from the PTT server 3 (S74: No). Upon
receiving a PTT end instruction (S74: Yes), the control unit 22 deletes
data in the in-use DTMF table (S75), and ends the PTT participation
process.

[0092] <2-2. PTT server 3>

[0093] The following describes the PTT server 3.

[0094] Specifically, the PTT server 3 is a computer system composed of a
microprocessor, a ROM (Read Only Memory), a RAM (Random Access Memory),
etc. The RAM stores therein a computer program. The PTT server 3 achieves
its function by the microprocessor operating in accordance with the
computer program.

[0095] FIG. 8 shows the internal structure of the PTT server 3.

[0096] As shown in FIG. 8, the PTT server 3 includes a communication unit
41, a storage unit 42, and a control unit 43.

[0097] The communication unit 41 communicates with the mobile telephone 2
via any of the base stations 4. The structure of each base station 4 and
the operation thereof are well-known; therefore, a description thereof is
omitted here. The communication unit 41 and the mobile telephone 2
communicate with each other via the communication network 5 including the
base stations 4. Hereinafter, a description of the use of the base
station 4 and the communication network 5 for each communication is
omitted to avoid repetition. Instead, it is simply described as "the
communication unit 41 and the mobile telephone 2 communicate with each
other" or "the PTT server 3 and the mobile telephone 2 communicate with
each other".

[0098] The storage unit 42 stores various pieces of information.

[0099] The control unit 43 performs overall control of the PTT server 3.

[0100]FIG. 9 is a flowchart showing a process pertaining to a PTT call,
the process being performed by the control unit 43 of the PTT server 3.

[0101] Upon receiving a PTT start request from the mobile telephone 2
(S91), the control unit 43 stores, into the storage unit 42, the
telephone numbers included in the PTT start request as the telephone
numbers of the mobile telephones constituting a PTT group (S92).
Subsequently, the control unit 43 transmits a PTT start instruction to
each of the mobile telephones constituting the PTT group (S93).

[0102] Upon receiving a right-to-speak acquisition request from any of the
mobile telephones 2 within the PTT group (S94: Yes), the control unit 43
determines whether the right to speak is assigned to any of the mobile
telephones 2 (S95).

[0103] If the right to speak is already assigned (S95: Yes), the control
unit 43 transmits, to the mobile telephone that has transmitted the
right-to-speak acquisition request (hereinafter, also referred to as
"right-to-speak requester") a notification indicating that assignment of
the right to speak has failed (S111), and proceeds to step S98 which is
described below. If the right to speak is not assigned yet (S95: No), the
control unit 43 assigns the right to speak to the right-to-speak
requester, and stores, into the storage unit 42, information indicating
the right-to-speak requester (S96). Then, the control unit 43 transmits a
notification indicating that assignment of the right to speak has been
successful to the right-to-speak requester (S97).

[0104] When DTMF information pertaining to a speaker is received (S98:
Yes), the control unit 43 transfers the DTMF information to the mobile
telephone of each receiver (S99).

[0105] When audio data pertaining to the speaker is received (S100: Yes),
the control unit 43 transfers the audio data to the mobile telephone of
each receiver (S101).

[0106] When a right-to-speak release request is received (S102: Yes), and
a mobile telephone that has transmitted the right-to-speak request is the
same as the right-to-speak requester indicated by the information stored
in the storage unit 42, the control unit 43 deletes the information, in
the storage unit 42, indicating the right-to-speak requester, so as to
make the right to speak available again (S103).

[0107] Also, upon receiving a PTT end request (S104: Yes), the control
unit 43 transmits a PTT end instruction to each mobile telephone within
the PTT group, and ends the process pertaining to a PTT call (S105).

<3. Operation>

[0108] FIG. 10 is a flowchart showing an overall process of the PTT system
1, during PPT execution pertaining to the present embodiment.

[0109] The following describes a case where the mobile telephone 2a of the
user A starts a PTT call after designating the mobile telephone 2b of the
user B and the mobile telephone 2c of the user C as belonging to a PTT
group.

[0110] Details of the operations of the mobile telephones 2a, 2b, and 2c
and the PTT server 3 are already described above. Accordingly, the
following mainly describes transmission and reception of information
among the mobile telephones 2a, 2b, and 2c and the PTT server 3.

[0111] First, the user A of the mobile telephone 2a operates the input
unit 14, and inputs a PTT start instruction.

[0113] The PTT start request includes the telephone number of the mobile
telephone 2a, and the telephone numbers of the mobile telephones 2b and
2c of the users B and C who are included in the PTT call.

[0115] Next, the mobile telephone 2a of the user A, who is a speaker in
the PTT call, detects a press of the PTT button by the user A, and
transmits a right-to-speak acquisition request to the PTT server 3
(S204).

[0116] Since the right to speak is not assigned to any of the mobile
telephones in the PTT group, the PTT server 3 assigns the right to speak
to the mobile telephone 2a (S205), and transmits, to the mobile telephone
2a, a notification indicating that the acquisition of the right to speak
has been successful (S206).

[0117] Upon receiving the notification indicating that the acquisition of
the right to speak has been successful, the mobile telephone 2a selects
DTMF information (value of which is "1"), acquires audio of the user A
and generates audio data from the audio (S207), and transmits the DTMF
information and the audio data to the PTT server 3 (S208).

[0118] The PTT server 3 transmits, to the mobile telephones 2b and 2c
within the PTT group, the DTMF information and the audio data received
from the mobile telephone 2a (S209 and S210).

[0119] Each of the mobile telephones 2b and 2c outputs, from the receiver
12, (i) a tone corresponding to the DTMF information, and subsequently
(ii) audio indicated by the audio data (S211 and S212).

[0120] At this time, if the user B presses the PTT button of the mobile
telephone 2b, the mobile telephone 2b detects the press of the PTT
button. Upon detecting the press, the mobile telephone 2b transmits a
right-to-speak acquisition request to the PTT server 3 (S213).

[0121] The PTT server 3 has already assigned the right to speak to the
mobile telephone 2a, and the right to speak has not been released yet.
Accordingly, the PTT server 3 determines that assignment of the right to
speak has failed (S214). Subsequently, the PTT server 3 transmits, to the
mobile telephone 2b, a notification indicating that acquisition of the
right to speak has failed (S215). The mobile telephone 2b receives the
notification from the PTT server 3, and recognizes that acquisition of
the right to speak has failed.

[0122] Next, the user A finishes speaking, and releases the PTT button.
Upon detecting the release of the PTT button, the mobile telephone 2a
transmits a right-to-speak release request to the PTT server 3 (S216).

[0123] The PTT server 3 releases the right to speak assigned to the mobile
telephone 2a (S217).

[0124] Here, the user B presses the PTT button of the mobile telephone 2b
again. Then, the mobile telephone 2b detects the press of the PTT button
by the user B, and transmits a right-to-speak acquisition request to the
PTT server 3 (S218).

[0125] Since the right to speak is not assigned to any of the mobile
telephones in the PTT group, the PTT server 3 assigns the right to speak
to the mobile telephone 2b which has transmitted the right-to-speak
acquisition request (S219). Subsequently, the PTT server 3 transmits, to
the mobile telephone 2b, a notification indicating that acquisition of
the right to speak has been successful (S220).

[0126] Upon receiving the notification indicating that the acquisition of
the right to speak has been successful, the mobile telephone 2b selects
DTMF information (value of which is "2"), acquires audio of the user B
and generates audio data from the audio (S221), and transmits the DTMF
information (2) and the audio data to the PTT server 3 (S222).

[0127] The PTT server 3 transmits, to the mobile telephones 2a and 2c
within the PTT group, the DTMF information and the audio data received
from the mobile telephone 2b (S223 and S224).

[0128] Each of the mobile telephones 2a and 2c outputs, from the receiver
12, (i) a tone corresponding to the DTMF information, and subsequently
(ii) audio indicated by the audio data (S225 and S226).

[0129] Here, the user A of the mobile telephone 2a operates the input unit
14, and inputs a PTT end instruction (S227). Then, the mobile telephone
2a transmits a PTT end request to the PTT server 3 (S227).

[0130] Upon receiving the PTT end request, the PTT server 3 transmits the
PTT end request to the mobile telephones 2b and 2c (S228 and S229), and
ends the PTT process.

<4. Modification>

[0131] Although description has been provided of the communication
terminal of the present invention based on an embodiment, the present
invention is not limited to the communication terminal described above.
For example, the following modifications are possible.

[0132] (1) In the above embodiment, an identification tone for identifying
a user is output before output of audio pertaining to a group call.
However, it is not limited to such as long as the user can be identified
by the identification tone.

[0133] For example, the identification tone may be output after the output
of the audio pertaining to the group call. Alternatively, the
identification tone may be output by overlapping part of the audio
pertaining to the group call, or may be output during a pause in a
conversation in the group call.

[0134] (2) In the above embodiment, a DTMF tone is converted into a tone
indicated by a note. However, it is not limited to such as long as the
DTMF tone is converted into a tone that assists identification of a user.
For example, the DTMF tone may be converted into another tone by which
identification of the user is considered to be easy. Examples of such a
tone include an animal sound, a wave sound, and a sound at a specific
frequency.

[0135] Also, the DTMF tone, which is indicated by the corresponding DTMF
information, may be directly output from the receiver 12, without being
converted into the tone indicated by the note. In this case, the DTMF
tone is output first, followed by audio indicated by audio data. Also,
the process of converting DTMF tone information to note information by
the control unit 22 is omitted.

[0136] Note that in the above embodiment, a DTMF tone is converted into a
tone indicated by a note such as Do, Re, or Mi, because a user may find
it more difficult to distinguish between different DTMF tones than to
distinguish between different notes such as Do, Re, and Mi.

[0137] (3) In the above embodiment, for example, when a DTMF tone is the
combination of a signal of 1209 Hz in the high group and a signal of 697
Hz in the low group, DTMF information has a value of "1" and corresponds
to the key of number "1" among the group of keys. However, it is not
limited to such.

[0138] For example, DTMF information may be an encoded tone obtained by
directly encoding a signal of 1209 Hz in the high group and a signal of
697 Hz in the low group. The above encoding may be performed using the
same method as the method for encoding audio pertaining to a call to
generate audio data. In this case, it is possible to collectively encode
a sequence of (i) the combination tone made up of a signal of 1209 Hz and
a signal of 697 Hz and (ii) audio pertaining to a group call. This
eliminates the need of encoding the DTMF tone separately from the audio
pertaining to the group call.

[0139] (4) In the above embodiment, when a PTT call is started by any of
the mobile telephones, the PTT call continues until a PTT end instruction
is input by the user of the mobile telephone. However, a different event
may trigger the end of the PTT call. For example, the PTT server may
detect a state where none of the PTT buttons of the mobile telephones is
pressed for a predetermined time period (e.g., 10 minutes), and may end a
PTT call upon the detection of that state.

[0140] (5) In the above embodiment, DTMF information is selected by each
mobile telephone in a predetermined order. Specifically, one of the
mobile telephones selects the DTMF information having a value of "1".
Next, another one of the mobile telephones selects the DTMF information
having a value of "2", and so forth. However, DTMF information may be
selected using a different algorithm as long as each mobile telephone can
select different DTMF information.

[0141] (a) For example, a random number may be generated when DTMF
information is to be selected. If the random number thus generated is not
used by another mobile telephone, the random number may be used as DTMF
information. If the random number thus generated is already used by
another mobile telephone, another random number is newly generated. The
above process of newly generating another random number is repeated until
an unused random number is generated.

[0142] (b) Also, all or part of unique information, such as a telephone
number allocated to the own mobile telephone, may be used as DTMF
information.

[0143] Alternatively, a unique number generated from such unique
information may be used as DTMF information.

[0144] (6) A control program composed of program code, in a machine
language or a high-level language, for causing a processor in each mobile
telephone, a processor in the PTT server, and circuits connected to the
processors to perform the processes described in the above embodiment and
modifications may be recorded onto a recording medium or distributed over
a variety of communication channels. Examples of such a recording medium
include an IC card, a hard disk, an optical disc, a flexible disk, a ROM,
and a flash memory. The control program that is circulated and
distributed is used by being stored on a processor-readable memory or the
like. The functions described in the above embodiment are achieved by the
processor executing the control program. Note that instead of directly
executing the control program, the processor may compile the control
program before execution or execute the control program with an
interpreter. Also, note that the present invention may be a method for
realizing each process described in the above embodiment and
modifications.

[0145] (7) The functional structural elements in the above embodiment and
modifications may be implemented as circuits that perform the functions,
or implemented by one or more processors executing a program. Also, the
functional structural elements may be realized as integrated circuit
packages such as ICs, LSIs or the like. These packages are incorporated
into various devices, whereby the devices realize the functions described
in the above embodiment.

[0146] (8) The above embodiment and modifications may be wholly or
partially combined.

INDUSTRIAL APPLICABILITY

[0147] The communication terminal of the present invention is suitable as
a terminal used in a system that realizes a group call, such as a PTT
call.